As large numbers of objects are moved in inventory, product manufacturing and merchandising operation, there is a continuing challenge to accurately manage the location and flow of objects. Additionally, there is a continuing goal to interrogate the location of objects in an inexpensive and streamlined manner. Furthermore, there is a need for tag devices suitably configured to mount to a variety of objects including goods, items, persons, or animals as well as any moving or stationary, animate or inanimate object. One way of tracking objects is with an electronic identification system.
One presently available electronic identification system utilizes a magnetic field modulation system to monitor tag devices. A controller interrogator unit creates a magnetic field that becomes detuned when the tag devices pass through the magnetic field. In some cases, the tag device may be tuned and detuned in a sequence unique to the tag device in order to distinguish between a number of different tags, each having a distinct identification sequence. Typically, the tag devices are entirely passive, eliminating the need for a portable power supply which results in a small and portable package. However, that identification system is only capable of distinguishing a limited number of tag devices, over a relatively short range, limited by the size of the resulting magnetic field. Detuning is the means of encoding the identification number of the tag device or its data.
Another identification system utilizes an RF transponder device affixed to an object to be monitored, in which a controller or interrogator unit transmits an interrogation signal to the device. The device receives the signal, and then generates and transmits a responsive signal. The interrogation signal and the responsive signal are typically radio frequency signals produced by a radio frequency transmitter circuit. Since radio frequency signals can be transmitted over greater distances than magnetic fields, a radio frequency based transponder device tends to be more suitable for applications requiring tracking of a tag device that may not be in close proximity to an interrogator unit. However, when a large number of devices are utilized, the interrogator unit triggers frequent wake up of each device. As a result, responsive signals are frequently generated. In the case of a battery powered device, the life of the battery is severely diminished due to frequent unintentional wake up of the device. Therefore, there is a need to produce tags having different receiver sensitivities, and to produce tags having either factory or user adjustable sensitivities.
Conventional heterodyne receivers down convert a radio frequency signal to a baseband signal using one or more intermediate stages in which the radio frequency signal is converted to one or more intermediate frequency signals, lower than the radio frequency signal, until the baseband frequency is reached. A heterodyne transmitter generates a higher radio frequency signal from a baseband signal using one or more intermediate stages to up convert the frequency. A transceiver provides both transmit and receive components and functions.
A homodyne receiver directly down converts radio frequency signals to baseband frequency without intermediate stages. Analogously, a homodyne transmitter up converts from baseband to radio frequency without intermediate stages. A radio system (frequency conversion stage, tuner, receiver, transmitter, or transceiver) may include homodyne and heterodyne components.
The trend in new radio systems technology receiver/tuner development is predicted to concentrate on moving the radio frequency spectrum down to baseband frequencies where it will be digitized and processed under software control. That will impose even more stringent demands for dynamic range, increased sensitivity, and lower distortion. Reducing size, weight and power consumption to provide longer operating time under battery power, are also concerns for commercial and non-commercial applications. A key system performance challenge involves keeping the spectrum dynamic range (sensitivity versus distortion) as high as possible before digitization and the analog to digital conversion, while maintaining high sensitivity and controlling distortion.
Thus, a need exists in the art to address the aforementioned deficiencies and inadequacies.